Unformatted text preview: least 620 MPa across the entirety of its cross-section. First of all, if the steel is heat treated so as to produce martensite or tempered martensite, there will undoubtedly be a variation of tensile strength over the cross-section. A better heat treatment would be an isothermal one. From Equation (6.20a) a tensile strength of 620 MPa corresponds to a Brinell hardness of about 180. Upon consultation of Figure 10.22(a), we note that for an alloy of composition of 0.40 wt% C, in order to achieve a hardness of 180 BHN, a microstructure of fine pearlite is required. In Figure 10.29 is shown an isothermal transformation diagram for a 0.45 wt% C alloy, which would be very similar to that for a 1040 steel. According to this diagram, we would want to austenitize the alloy at approximately 800∞C, rapidly cool to about 600∞C, and hold the alloy at this temperature for on the order of at least 3 s, after which it is cooled to room temperature....
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- Tensile strength, Austenite, HRC, equivalent distance